Ethylene interpolymer products are used in caps and closure applications to produce a wide variety of manufactured articles, e.g. caps for carbonated or non-carbonated fluids, as well as dispensing closures including closures with a living-hinge functionality. Such caps and closures are typically produced using conventional injection or compression molding processes. The ethylene interpolymers disclosed herein, having melt index ≧0.4 dg/min to ≦5.0 dg/min, have a G′[@G″=500 Pa] that is advantageous in compression molding processes, i.e. a G′[@G″=500 Pa] from ≧40 Pa to ≦70 Pa. Further, ethylene interpolymers disclosed herein, having melt index >5.0 dg/min to ≦20 dg/min have a G′[@G″=500 Pa] that is advantageous in injection molding processes, i.e. a G′[@G″=500 Pa] from ≧1 Pa to ≦35 Pa.
In caps and closure markets there are constant needs to develop new ethylene interpolymers having improved properties. Non limiting examples of needs include: stiffer caps and closures (higher modulus) that allow the manufacture of thinner and lighter weight caps and closures, i.e. improved sustainability (source reduction); higher heat deflection temperatures (HDT) which expands the upper use temperature of caps and closures and is advantageous in hot fill applications; faster crystallization rates which allows caps and closures to be manufactured at higher production rates, e.g. more parts per hour, and; improved Environmental Stress Crack Resistance (ESCR), particularly for caps and closures used in chemically aggressive environments.
The ethylene interpolymer products disclosed are produced in a solution polymerization process, where catalyst components, solvent, monomers and hydrogen are fed under pressure to more than one reactor. For ethylene homo polymerization, or ethylene copolymerization, solution reactor temperatures can range from about 80° C. to about 300° C. while pressures generally range from about 3 MPag to about 45 MPag and the ethylene interpolymer produced remains dissolved in the solvent. The residence time of the solvent in the reactor is relatively short, for example, from about 1 second to about 20 minutes. The solution process can be operated under a wide range of process conditions that allow the production of a wide variety of ethylene interpolymers. Post reactor, the polymerization reaction is quenched to prevent further polymerization, by adding a catalyst deactivator, and passivated, by adding an acid scavenger. Once passivated, the polymer solution is forwarded to a polymer recovery operation where the ethylene interpolymer is separated from process solvent, unreacted residual ethylene and unreacted optional α-olefin(s). Further, the ethylene interpolymer products disclosed herein are synthesized using at least two reactors employing at least one single-site catalyst formulation and at least one heterogeneous catalyst formulation.